Recently, various display devices have been actively developed as replacements for cathode ray tube display devices. Since compared with others liquid crystal display (LCD) devices are light in weight, thin in thickness and low in power consumption, they are widely used in many applications. Active matrix type liquid crystal display (AMLCD) devices are particularly main-stream products in such LCD devices because pixels of the AMLCD devices each include switching elements to separate electrically enabled pixels from disabled ones, the enabled pixels hold video signal supplied to them. It is because no cross-talk takes place between adjacent pixels and the AMLCD devices display good quality images. A transparent type AMLCD device provided with thin film transistors as switching elements will be explained by way of example. The AMLCD device includes a liquid crystal layer held between circuit array and counter substrates through alignment films attached to their inside surfaces. The circuit array substrate includes a transparent substrate made of glass or quartz, signal and scanning lines disposed in a matrix on the substrate, an insulation film to isolate the signal lines from the scanning lines, and transparent pixel electrodes made of indium-tin-oxide (ITO) films provided at elements of the matrix. Thin film transistors each are disposed as switching elements to control the pixels at vicinities of intersecting points in the matrix. Gate and drain electrodes of the transistors are connected to the scanning and signal lines, respectively, while source electrodes are connected to the pixel electrodes.
The counter substrate includes an ITO counter electrode formed over the transparent substrate and a color filter layer for color image displays. The circuit array substrate extends a shelf-like portion used for a connecting edge section to the outside of a sealing area of the LCD device. The shelf-like portion is provided with connecting pads to which input terminals for outer drive circuits are connected. The connecting pads are made of extending portions of the scanning and signal lines. The liquid crystal layer held between the circuit array and counter substrates is sealed by a sealant at their frame edges.
Recently, in order to expend the formation area of pixel electrodes, the pixel electrodes are arranged on a thick insulation resin film to insulate the pixel electrodes from signal or scanning lines and surroundings of the pixel electrodes are overlapped with these lines. The thickness of such an insulation resin film is generally 1 μm to 10 μm and, preferably, 2 μm to 4 μm. Further, the insulation resin film is a low dielectric constant organic resin so that the pixel electrodes and the signal and scanning lines overlapped with them through the insulation resin film form small electric capacitances and electric short circuits between them occur only as a remote possibility.
Usually, the circuit array substrate in these display devices requires naked sections where such a thick insulation resin film is removed to expose the connecting pads provided at the connecting edge section of the circuit array substrate. The connecting pads extending from the signal and scanning lines are connected to output terminals of a tape carrier package (TCP). The output terminals of the TCP are pin-like ones provided for a high resolution display and easy assembling and their hooks or thicker edge portions, for example, are engaged with the connecting pads. When the AMLCD device is assembled with the TCP, however, electric short circuits occur between adjacent terminal pins of the TCP at times. Carefully analyzing possible causes for the electric short circuits, the inventor has discovered that electrically conductive layers of the pixel electrodes remain strip-like at outer portions of the connecting pads without etching.